Control for free piston engines



CONTROL FOR FREE PISTON ENGINES Filed May 24, 1950 INVENTOR. l/V/Wa/"dA. Mara/n H TTOPNEYS Patented Jan. 22, 1952 UNITED STATES PATENT OFFICE=-2,-583,115 CONTROL FOR FREE ris'roN'ENemr's Willard A. Morai'n,Hamilton, Ohio, assignor, by

mesne assignments, to Baldwin-Lima-Hamil- 'ton Corporatiomacorporation=of Pennsylvania 'KpplicationMayM, lssofseriarno.163,974

"4 Claims. (01. 123-46) This invention relates to free piston internalcombustion engines and is particularly directed 'to a siinplifiedmeohanism -foreontrolling the return-'strokeof the pistonsin suchaneng'ine.

I n the operation of free pistonengines, some means inust be provided toreturn the pistons to the'pro'per position'within the enginecylinder'for oo'n'iiii ess'ion or the change' of ai r therein. Where-the engine is used on'a p'art of'an air compressor operating atconstant load, the re-expansion eny of theair in the compressor may be-utilizecl to return the pistons. However, in the case of the enginebeing used as a power gas generator and operating at variableload, it isnecessary to resort to the useof an additional cylinder or chamberwherein the proper .piston restoringenergy can be developed. Such a,chamber is known asa bounce chamber, and by-adding air to or ventingthis chamber it is possible to govern "the inward piston stroke withinrelatively close limits.

It is known in the art toaccomplish control of the bounce chamber energyin various ways. 'See, for example, the patent to -Lewis;2,4=3 5,970.The present invention is primarily directed to a simplified controlstructure in which the bounce chamber energy is related to theloadon theen- :gine, the latter being reflected in "a change in exhaust pressure.I

I The primary object of the invention ie to provide a control device ofthe above character whiehissimple-andefiicient in operation and which isnot likely to get out of adjustmenta'fte'r long continued use. v

Another object of 'the invention is to provide a control for a Spowergasgenerator that is operated in conjunction with a turbine of hired noz-'zle area, the control being arranged to corr late gas generator bounce"pressure a'n'd 'eihaus't to frfai'titai'n proper stroke length in thegas "gen- "er ator. g V g g I other objects'and advantages or theinvention will "become apparent from the following specification,reference being had to the accom an ing drawings in'which: f

Fig. 1 is"a diagrammaticvi-ewj aruy i'nseoti on, of a free piston engineembodying the present "contra device; I

v Fig. 2 is a'central'verticalsectional view somewhat diagrammatic, of'a suitable control deviceenib'odying' the invention and Fig. 3 is "afragmentary sectional'view of a modmention introducing additional'CO'ntlol ressure.

feliing to the erawings, the present iriVen- "flail is shown inconnection "with 2. ires piston '2 'power gas generatordesignatedgenerally =1 0, "h'avi'ri'g'a't 'e'a'chenda bounce chamber H connectedb'y-an equalizing line 12. The-gasg-e'nerajtor includes the usualintegral multiple pistons fitt'ing in power cylinders M, compressorcylinders l-il and the bounce cylinders or chambers H. The compressorcylinder 16 is also utilized as a reverse bounce chamber H in a mannerset forth in the above identified Lewis patent. it will be appr'e ciatedthat, if the *engine is to operate broompres'sion ignition the powerpistons must reach an inward pointsuch that the air'betweenthe'm is atthe proper temperature and pressure "to ignite "an injected fuel charge,but must not approach each other'too closely, thereby restricting thevolume into which the fuel may be injected or 'raisingthe temperatureand pressure of the air charge beyond practical limits. Excessive"pressure in the bounce chambers will also tend to stall the engine byrestricting the'length of the outward strokes of the piston's'andpreventing proper scavenging of the power cylinder. It is therefore,important that the energy available in the bounce chambers for returningthe pistons be maintained at the proper level'required for a given loadcondition. Further, it is not desirable that the devices intendedtocontrol the piston restoring energy be responsive to each minute "changein stroke length, since such devices will exhibit a tendency to huntabovea'nd below the proper 'ener y level. It is *sufiicient that pro"-nou'n'ced trends toward changes in stroke length 'be followed, 'so that"the present invention in'tr'oducesfoscillation clamping means in thecontrol circuit.

"The present invention comprises regulating valvemeans constructed andarranged to 've'n'to'r add air to the bounce chambers as the engineexhaustpressure decreaseso'r increases. Broadly, control of the strokelength of'a free piston engine by regulating the quantity "of air inbounce chamber is known in "the are-but prior devices have relied 'oncomplicated equipment to balance pressures in various engine chambers,and have proved di'fiicult'to adjust'an'd maintain.

The valve means of the present invention'is'im dicated somewhatdiagrammatically in 'Fig. 2 and comprises a body 20 having an upperconnection 22 to the engine-exhaustline/aconnection 24- to a source ofhighpressur'e air-such as a 'storage bottle -25, and twoco'nnection's, 28'and 30, 'to the bounce c linder equalizing line 1 2.

Connection 28 is deliberately restricted ''so that small fluctuations donot aifec't the control ele' r'rieiits. The damped" con'n'ection thusprovided permits the control to respond to variations in the meanpressure in the bounce chamber equalizing line and not to the maximumand minimum pressures therein. No attempt has been made to indicate themanner in which the valve body is assembled.

A cylinder 32 at the top of the valve body 20 communicates directly withconnection 22, and a piston 34, working in this cylinder is thussubjected to the control pressure which may be either exhaust pressure,or the sum of exhaust and reverse bounce pressures, at all times. Piston34 is biased inwardly of its cylinder by a regulating spring 36interposed between an extension 31 of the piston and a head 38 of amovable valve seat 40. Head 38 is attached at the center of a diaphragm42, the outer edge of which is sealed in the body 26.

The movable valve seat 40, of which head 38 forms the upper end, isguided for linear movement in a bore 44 of the body 20, by a packedpiston-like flange 46 and is provided with a central passage 48 whichopens into a vented chamber 50 above the diaphragm. A valve 52 normallycloses passage 46 by sealing engagement with the lower end of themovable valve seat 48.

Valve 52 is preferably provided with a guiding stem 54 which cooperateswith a suitably formed part of the body 29 to assure linear movement tothe valve. The valve is biased upwardly by a spring 56 interposedbetween a plate valve 58 and a stationary body part Bil, the plate valveengaging a stem extension 62 of the valve 52. Valve 52 is limited in itsupward movement by a series of projections 64 extending into the bore :3

44 in the path of movement of the valve.

A chamber 66 around valve 52 communicates with damped connection 28 tothe direct bounce cylinder equalizing line 12 by means of passages 68and 12. Thus, when the valve is opened by a separating movement ofseatand the head of the valve, chamber 66 and hence the bounce cylinderswill be vented through passage 48 and chamber 50.

Passage l2 in the body 20 opens into a chamber '14 below the diaphragm42 so that the underside of the diaphragm is subjected to the existingmean pressure in the bounce cylinder equalizing line and is urgedupwardly thereby. This force is opposed by the force exerted by thecontrol pressure acting on piston 34 and transmitted through spring 36and head 38. Proper selection of the relative areas of piston 34 anddiaphragm 42 makes it possible to provide a control suitable for a widerange of systems, primary dependence being on the operatingcharacteristics of the associated turbine or other gas consumer.

Suitable means are also provided to add air to the bounce chambers byopening communication between high pressure air connection 24 and bouncecylinder charging line 30. This connection is controlled directly by alower valve 80 disposed in a chamber 82 in the body 20, the chamber 82being constantly connected to the source of high pressure air.

Lower valve Bil is carried by a stem 84 formed on the lower side of apiston 86 working in a cylinder 88 in the valve body. The stem 84 has acentral passage 90 extending through it which communicates with thecylinder 88 above the piston 86, but the passage is restricted at itsupper end, as by an orifice 92. The lower face of piston 86 is subjectto the pressure of chamber 82 and the charging air by reason of adirect- 1y connecting passage 94. Thus, the upper and lower faces of thepiston are under the same pressure when conditions are'stable, but ifcylinder 88 were suddenly vented and pressure in the upper piston facerelieved, it will be seen that the pressure on the lower piston facewould predominate until air passing through the restricted end ofpassage 90 could again fill the cylinder to the initial pressure. Undercertain conditions of unbalanced pressure, then, piston 84 movesupwardly in its cylinder and charging valve 80 is opened. A spring 96biases the piston downwardly to close valve 80 when the pressures againbalance on the upper and lower faces of piston 86.

Cylinder 88 is controlled at its upper end by plate valve 58, and isvented, when this valve is opened, through passage 10, into the bounceair control circuit. The cylinder could be vented to atmosphere, but itis preferred to conserve the available air.

In operation, assuming the power gas generator to be running at normalstroke and frequency properly to supply gas to an associated turbine T,the control device above described will come into operation only upon adeviation from the proper operating conditions. If the control pressurerises for any reason the pressure in top cylinder 32 rises and piston 34moves outwardly against the tension of regulating spring 36. Diaphragm42 is thus lowered and the movable valve seat 40 and its associatedvalve 52 are likewise lowered so that plate valve 58 is opened whilevalve 52 remains closed. This condition would also be realized if forany reason the bounce spaces become undercharged and limited thepressure under diaphragm 42.

When plate valve 58 leaves its seat, air in lower cylinder 88, beingunder full supply pressure, rushes into the control system throughpassages 10 and I2. The forces On the two faces of lower piston 86 arethus unbalanced, there being a greater pressure on the lower face thanon the upper. The piston is thus moved upwardly in its cylinder and thelower valve is moved off its seat against the action of spring 96. Highpressure air from the storage bottle 26 thus enters the bounce chamberequalizing line and the bounce cylinders themselves. Thus more energybecomes available to force the engine pistons towards each other on thecompression stroke, compensating for the increased exhaust pressure orscavenging air.

As the bounce pressure is raised to the point where the desired balanceis again reached, the pressure on the under side of diaphragm 42 forcesthe diaphragm and its associated movable valve seat 40 upwardly allowingspring 55 to again seat plate valve 58 and prevent further escape of airfrom lower cylinder 88. As air from the high pressure source continuesto pass through passage and the restriction 92, the pressure above andbelow lower piston 86 soon becomes balanced and spring 96 can move thepiston and valve 80 downwardly to seat the latter and closecommunication to charging line 30.

If for any reason the exhaust pressure is reduced from the normaloperating condition, or if for any reason the bounce cylinders becomeovercharged, diaphragm 42 is moved upwardly to compress spring 38 due tothe now excessive pressure on its under face. The movable valve seat 40is thus moved away from valve 52 since the valve can follow the seatonly to the limit determined by the projections 54 in the bore 44. Sincepassage 48 is now open, venting into chamber 50 and to atmosphere cantake place from the bounce cylinder equalizing line through dampedconnection 28, passages 72, and 68. As the pressures are again balanced,diaphragm 42 will return to its normal position and valve 52 will againclose.

It will thus be seen that the bounce energy will be adjusted inaccordance with changes in load as reflected in a variation of theexhaust pres- L sure and, at any given load condition, will be correctedfor under-charge or over-charge resulting from any other cause such asleakage past the pistons, etc.

In the modification shown in Fig. 3, additional control pressure isintroduced by extending a line I00 from a reverse bounce equalizing lineI02 connecting the two reverse bounce chambers ll. The line I00 isconnected to the top cylinder 32 which is now broken down into twoaxially concentric cylinders 32, 32a. Cylinder 32 is connected to theexhaust line through conduit 22 while cylinder 32a is connected by lineI00 to the reverse bounce equalizing line. Piston 34 is now shown as astepped piston comprising a lower portion 34a operating in cylinder 32aand an upper portion 34 operating in cylinder 32. The composite pistonis thus subjected to the sum of the reverse bounce pressure and theexhaust pressure and a significant variation in either will causeoperation of the elements heretofore described to increase or decreasethe bounce pressure of the engine. If the reverse bounce pressure isincreased the frequency of operation of the engine is likewise increasedin accordance with the disclosure of Lewis Patent 2,435,970. An increasein reverse bounce pressure causes an increase in the direct bouncepressure but operation of the present engine with the over-all eiTectthat the engine runs at a higher frequency and greater load and suppliesconsiderably more gas to the turbine or other consumer.

The addition of control by means of the reverse bounce pressure is alsoadvantageous in the event that the system includes more than a singlefree piston power gas generator since control of the frequency ofoperation is more readily obtainable by variation in the reverse bouncepressure than by any other means so that more accurate synchronism canbe maintained between a multiplicity of gas generators.

While the invention has been disclosed in connection with a particularform and disposition oi! the parts numerous modifications and changesmay be made without departing from the scope of the appended claims.

What I claim is:

1. In an apparatus for controlling a free piston engine having a chamberin which air is compressed by a movement of the free pistons andsubsequently utilized to return energy to the system by re-expansion,the improvement comprising an element subject on one side to the averagepressure in said chamber and on the opposite side to a second pressurewhich reflects an op-- erating characteristic of the free piston engine,a valve seat attached to and movable with said element, a valve normallyclosed on said valve seat and disposed to follow the movements thereof,means to limit the movement of said valve in one direction to eifect aseparation of said valve and seat upon continued movement of said seatin one direction, a second valve opened by movement of said first valvein the opposite direction, and means operated in response to an openingof said second valve to admit air to said chamber.

2. The improvement defined in claim 1 in which said last means includesa cylinder in communication with a source of high pressure air, and apiston controlled valve normally closing communication between saidcylinder and said engine chamber, said piston controlled valve normallyclosing communication between said cylinder and said engine chamber,said piston controlled valve being opened when said second valve isopened.

3. The improvement defined in claim 1 in which said element comprises adiaphragm urged in one direction by pressure in said engine chamber andin the opposite direction by a pressure corresponding to engine exhaustpressure.

4. The improvement defined in claim 1 in which said element comprises adiaphragm urged in one direction by pressure in said engine chamber andin the opposite direction by a pressure corresponding to the sum ofengine exhaust pressure and pressure in an engine reverse bouncecylinder.

WILLARD A. MORAIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,053,720 Huck Sept. 8, 19362,077,802 Martin Apr. 20, 1937 2,352,891 Graves July 4, 1944 2,434,280Morain Jan. 13, 1948 2,467,513 Welsh Apr. 19, 1949

